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Venus Williams' dream of third U.S. Open title ends after loss to Angelique Kerber

Defending champion, Samantha Stosur is safely through to the fourth round of the U.S. Open after a straight-sets victory over 31st seed Varvara Lepchenko on Friday.

The Australian had to fight hard against the American in the first set but had an easier time of it in the second eventually prevailing 7-6 (7/5) 6-2.

"As the match went on I got a little more comfortable and relaxed a little bit more. In the first set I felt like I served really well. That's how I was able to get into those games in the second set," Stosur said.

The seventh seed now faces British teenager Laura Robson, who continued her remarkable run with victory over ninth seed Li Na of China.

After seeing off three-time U.S. Open champion Kim Clijsters on Wednesday, Robson repeated the trick against Na on Friday, winning 6-4 6-7 (5-7) 6-2.